The present invention relates to a storage system that performs data storage control on storage devices such as a hard disk drive (hereinafter referred to as a “HDD”).
In accordance with the increase in the amount of data managed in a computer system including a storage system, and a server and host computer connected to the storage system via a communication path such as a network, the amount of the storage extents in the storage system has been increasing. In a storage system, a volume a host computer can access is logically defined, and the host computer can perform data input and output to/from a storage device by accessing a physical storage extent included in the logical volume.
Recently, because the data amount managed by a host computer has increased considerably, the volume size, being the storage capacity of a volume, has to be increased to a large extent. If a large-sized storage extent is allocated in advance to a host computer, shortage of storage capacity for the host computer does not occur, and therefore, the storage extent size allocated to the host computer does not have to be extended in the middle of processing. However, if a host computer does not use so much data, part of the storage extent allocated to the computer will remain unused, and that unused storage extent is wasted. Therefore, JP-A-2005-11316 proposes allocating an actual storage extent to an extent in a virtual volume in a storage system when a processor in a host computer writes data to that virtual volume. U.S. Pat. No. 6,823,442 discloses providing a storage system with a virtual volume that is to be accessed by a host computer and allocating a physical storage extent to that virtual volume.
Conventional examples concerning the present invention include JP-A-2005-128771, which relates to a data file system including a data access server with physical storage for storing data, that accesses the physical storage when receiving an access request; and a data file server that sends an access request to the data access server and performs data filing by using the data access server for data storage, and in which a physical block is effectively released when a logical block becomes unnecessary. JP-A-2004-127301 discloses a storage system including a virtual storage space, a physical storage space, a mapping system configured to associate a plurality of addresses in the virtual storage space with respective addresses in the physical storage space, and a controller configured to automatically remove a portion of the mapping system according to a priority specification for designating the portion to be removed of the mapping system according to the order.